1. Field of the Invention
The present invention relates to joints and springs, and more specifically relates to moveable joints and springs for mechanical systems and medical devices such as intervertebral implants and knee implants.
2. Description of the Related Art
A joint is a structure that joins together two separate parts. Some joints unite the two parts rigidly, however, other joints permit motion between the two parts. Some joints are reinforced with nails, screws, or glue, such as a joint forming a connection between two pieces of wood or metal.
In a human body, a joint is the moveable or fixed place where two bones or elements of a skeleton are joined together. Recently, moveable artificial joints have been incorporated into medical implant devices such as artificial knees, artificial hips, and spinal implants such as intervertebral discs. By 2012, the joint reconstruction market is expected to grow from $12.2 to $17.4 billion. By 2016, the spinal implant market is expected to grow from $6.5 to $10.3 billion.
Metal rods and pedicle screws are often used during spinal fusion procedures. Physiological drawbacks of using metal rods for spinal fusion include decreased motion, pain, degeneration of joints, stiffness, epidural searing and muscle stripping. Other drawbacks include the high costs associated with physical therapy and rehabilitation, and instances of post-surgical infection.
One problem with joints for mechanical systems and medical devices is that they tend to wear out and must be replaced. Other problems include gel extrusion, joint/surface friction and bone resorption. Another problem is that joints do not sufficiently dampen vibrational, compression and tension forces, resulting in energy losses and the generation of excessive noise. In addition, moveable artificial joints do not accurately replicate the natural movement of the human body.
In view of the above problems, there remains a need for improved joints for mechanical systems and medical devices that are durable, conserve energy, sufficiently absorb vibrational, compression and tension forces, and minimize noise. Moreover, there is a need for hydromagnetic joints that increase physiological effectiveness by increasing motion, and decrease friction and pain, and that decrease research and development and material costs, and increase durability.